Stable giant fullerenes

News

Scientists in China and Russia have succeeded in preparing the most stable isomers of the giant fullerenes C102 and C104, which they proved by X-ray crystallographic study of their chlorides.

For maximum stability, each pentagon in a fullerene must be surrounded by hexagons, following what has been dubbed the isolated pentagon rule (IPR). Recently, it was shown that reacting fullerenes with chlorine endowed them with sufficient stability that they could be isolated and characterised.

In the new study reported in Chemistry - A European Journal, the researchers produced fullerenes by setting a dc discharge arc on a graphite rod and separating the fullerene products by HPLC before chlorinating them in a sealed ampoule with VCl4 and SbCl5 for 2-12 weeks. The crystalline products were isolated and studied by X-ray diffraction.

The most stable IPR isomers C102(603) and C104(234) were confirmed. For the former, both the C102(603)Cl18 and C102(603)Cl20 compounds were detected, that with Cl20 being favoured due to the formation of an extra benzenoid ring and two C-C double bonds. C102(603) is the first IPR isomer of the C102 fullerene to be confirmed experimentally.

Similarly, the existence of C120(234) was verified from the X-ray diffraction studies of the C120(234)Cl16-22 compounds. Chlorination in all of them occurred at the para positions of isolated aromatic groups or at isolated C-C double bonds.

The isolation of these giant fullerenes will allow chemists easier access to allow their chemistry to be investigated, even though they take weeks to prepare.